Assessment of Storage Potential of Onion Varieties Using Variables Extracted from a Mathematical Model 4-Parameter Hill Function (4-PHF)

Onion seeds are prone to rapid germination and viability losses under unfavourable storage conditions. The final germination percentage is considered the most important parameter for determining the performance of seed lots after storage, although other quantitative traits, such as the time and speed of germination, help in more realistic predictions of seed germination. A study was conducted on seventeen seed lots of onion seeds to delineate the most comprehensive parameter indicating seed performance after storage using the four-parameter Hill function (4-PHF) mathematical model. Seeds of seventeen onion cultivars were subjected to accelerated ageing at 42 °C and 100% RH for 48, 96 and 144 h, followed by seed germination evaluation. The germination performance was evaluated by 4-PHF based on time-related parameters, such as the time to maximum germination rate (TMGR), time to 50% germination (T50), and uniformity (U), along with the germination percentage (a), shape and steepness of the Four-Parameter Hill Function (FPHF) curve (b), which were important determinants of the area under curve (AUC), and RoG (rate of germination) curves. Among the parameters, the AUC was found to provide the most comprehensive evaluation of the storage performance of the onion varieties and was decisive in the classification of the varieties as ‘good’ or ‘poor’ storers. A positive correlation between seed vigour index-I (SVI-I) and the AUC reiterated the suitability of using 4-PHF parameters for the assessment of the storage potential of onion varieties.